Fibromyalgia Syndrome is a disabling musculo-skeletal disorder of unknown etiology. A number of clinical features of fibromyalgia resemble those seen in patients with hypoadrenalism, or during steroid withdrawal, including fatigue, muscle and joint pain, depression, and impaired sleep and cognitive function. The similarity of symptoms has led us and others to hypothesize that there is relative or absolute adrenal insufficiency in fibromyalgia. Several preliminary reports indicate decreased adrenal function in fibromyalgia, and similar hypotheses have recently been postulated in patients with Chronic Fatigue Syndrome (CFS), a syndrome with many clinical similarities to fibromyalgia. In this study, we propose to test the hypothesis that patients with fibromyalgia have inappropriately low basal adrenocortical activity and to determine the site or sites of abnormality that account for this difference. Studies will compare the activity of the hypothalamic- pituitary-adrenal (HPA) axis in patients with fibromyalgia with HPA axis activity in matched normal healthy subjects and in patients with CFS. In these studies we will determine the circadian and pulsatile secretion of ACTH and adrenal steroids under basal conditions, determine the relationship between HPA axis activity and sleep disturbances, determine whether exacerbations in clinical symptomatology are associated with decreases in adrenocortical activity, and determine the responsiveness to specific stimuli of the adrenal, the pituitary and the hypothalamic- pituitary portions of the HPA axis.